At present, underground pipelines are commonly built by laying ready-made pipes inside a hole. Each pipe is placed into the hole by pulling it tt--therein with a winch.
The basic disadvantage of this method lies is that it often cannot be employed under the cramped city conditions where an areaway (pit) must be made at the hole inlet, the dimensions of this areaway corresponding to the length of the pipe to be laid into the hole.
Besides, excavation of areaways involves extra expenditures.
Another disadvantage of this method lies in the complexity of jointing the pipes inside the hole, all the more so when these holes have a considerable length.
Still another disadvantage of this method is the process of pulling pipes into holes whose length exceeds 20 m which becomes considerably more difficult and necessitates making holes with a diameter substantially larger then that of the pipe; this likewise involves additional expenditures. Besides, this method cannot be used with holes having curved portions.
Another, not less known method of forming casings in holes consists in making these casings in the course of hole driving. In this case the casing is made by the same device which is used for driving the hole. The casing is formed by the tail portion of the device body for which purpose the tail portion of said device is provided with channels for the delivery of the forming material, i.e. mortar, into the gap between the body of the device and the walls of the hole (see, for example, U.S. Pat. No. 2,680,416, Cl. 61-72.2, USA).
The main disadvantage of this method resides in the difficulties involved in ensuring the differential supply of the forming material to suit the hole driving speed which varies with the changing properties of the soil. As a result, the casing of the hole becomes nonuniform in density along the length of the hole, and has pits so that the casing walls differ in strength, permeability to moisture, etc.